# Documentation

### This is machine translation

Translated by
Mouseover text to see original. Click the button below to return to the English verison of the page.

# departure

Departure of longitudes at specified latitudes

## Syntax

```dist = departure(long1,long2,lat) dist = departure(long1,long2,lat,ellipsoid) dist = departure(long1,long2,lat,units) dist = departure(long1,long2,lat,geoid,units) ```

## Description

`dist = departure(long1,long2,lat)` computes the departure distance from `long1` to `long2` at the input latitude `lat`. Departure is the distance along a specific parallel between two meridians. The output `dist` is returned in degrees of arc length on a sphere.

`dist = departure(long1,long2,lat,ellipsoid)` computes the departure assuming that the input points lie on the ellipsoid defined by the input `ellipsoid`. `ellipsoid` is a `referenceSphere`, `referenceEllipsoid`, or `oblateSpheroid` object, or a vector of the form ```[semimajor_axis eccentricity]```.

`dist = departure(long1,long2,lat,units)` where `units` defines the angle units of the input and output data. In this form, the departure is returned as an arc length in the units specified by `units`. If `units` is omitted, `'degrees'` is assumed.

`dist = departure(long1,long2,lat,geoid,units)` is a valid calling form. In this case, the departure is computed in the same units as the semimajor axes of the ellipsoid.

## Examples

collapse all

On a spherical Earth, the departure distance is proportional to the cosine of the latitude. For example, calculate the departure distance for 0°.

`distance = departure(0, 10, 0)`
```distance = 10 ```

Now calculate the distance for 60°.

`distance = departure(0, 10, 60)`
```distance = 5.0000 ```

When you calculate the same departure distances on an ellipsoid, the result is more complicated. Again, calcuate the departure distance for 0°.

`distance = departure(0, 10, 0, referenceEllipsoid('earth', 'nm'))`
```distance = 601.0772 ```

Now calculate the distance at 60°. You can see that the value is not exactly half the 0° value.

`distance = departure(0, 10, 60, referenceEllipsoid('earth', 'nm'))`
```distance = 301.2959 ```

collapse all

### Departure

Departure is the distance along a parallel between two points. Whereas a degree of latitude is always the same distance, a degree of longitude is different in length at different latitudes. In practice, this distance is usually given in nautical miles.